Internal combustion engines are run on a variety of different types of fuels including gasoline, alcohol based fuels and heavy fuels such as diesel fuel, JP5, JP8, Jet-A and kerosene. Typically, gasoline powered or fueled engines operate at compression ratios of approximately 10 to 1 to as low as 5 to 1 whereas diesel and other heavy fuel engines generally require much higher compression ratios, typically on the order of 17 or 20 to 1. This difference in compression ratios is due to the different types of ignition systems used for gasoline engines versus heavy fuel engines.
For example, gasoline, which has a relatively low boiling point of approximately 135.degree. F. at sea level, readily forms vapors in air at atmospheric pressure, such that gasoline fueled engines typically can be spark ignited and operate with a stoichiometric air-fuel ratio. Heavy fuels, by contrast, have higher boiling points, i.e., approximately 350.degree. F. at sea level for diesel fuel, and therefore heavy fuels such as diesel fuel do not readily form such vapors under ambient conditions, making ignition of heavy fuels with spark ignition systems difficult. Thus, heavy fuels generally are used in compression ignition engines in which the fuels are injected under very high pressures or compression loads to generate sufficiently high heats of compression in the engine cylinder to raise the temperature of the air in the engine cylinder above the ignition point of the heavy fuel. The fuel is then vaporized and burned in the heated air in the cylinder to drive the engine. The HIGH boiling point of heavy fuels makes them less volatile so that these fuels do not readily form vapors at ambient temperatures, making such fuels impractical for use in typical spark ignition engines. For example fuels like kerosene are sometimes used in spark ignition engines, but only after the engine is started with gasoline and operated to raise the engine temperature to a point where vaporization of the kerosene fuel can occur.
The high compression loads resulting from the combustion of heavy fuels also places significant strain on the engine components, requiring such engine components to be formed from thicker, heavier materials to withstand these high compression loads. Since gasoline does not require high compression ratios, with their resultant high compression loads, gasoline engines typically can be lighter, smaller and more portable than heavy fuel engines that produce comparable horsepower but which require significantly heavier, larger engine components in order to be able to withstand the high compression ratios generally required to ignite heavy fuels.
As a result, most heavy fuel powered applications are limited to large, heavy compression engines such as are found in large vehicles such as trucks. Gasoline engines, which can be smaller and lighter in weight, generally are used for smaller applications such as generators and fans or blowers or similar applications for ease of portability and use. For example, the military uses a number of different types of small, light weight gasoline powered engines for use as generators, fans and blowers, pumps, including pumps for fire suppression systems, and other applications such as M17 portable decontamination units for use in the field. Heretofore, diesel or other heavy fuel powered engines have been impractical for use in such applications in the field where portability and ease of storage are necessary, due to the larger sizes and significant weight of such heavy fuel engines.
The problem with gasoline powered engines is, however, that the ability of gasoline to readily form vapors in ambient air at low atmospheric pressure, which enables easy ignition, makes gasoline extremely volatile and dangerous to handle and use as a stray spark and even excessive heat can ignite the gasoline vapors. In addition, in many applications in fields such as construction or military operations, diesel fuel or other heavy fuels are readily available and are used for vehicles such as heavy trucks, bulldozers and the like, whereas gasoline must be brought to the site in containers and stored as a hazardous material.
For example, on Navy ships the engines and most heavy pump or turbine systems are driven using diesel fuel and typically the only use for gasoline on these ships is for the pumps for fire suppression systems, which are required to be light weight and small in size so that they can readily be carried through doors and to various locations throughout the ship. The gasoline is, however, among the most dangerous and volatile materials on the ship. In addition, the military has indicated a desire to standardize the fuel used for all applications, with its preference to being a use of lower cost, safer to handle and use heavy fuel such as JP8 or diesel and to avoid the use of different types of fuels for different applications, especially the use of gasoline due to its volatility and handling requirements for use in the field. It is still necessary, however, for the engines for applications such as pumps and decontamination units to be light weight and easily portable.
Attempts further have been made to develop igniters that can generate sufficiently high heats of combustion sufficient to ignite heavy fuels without requiring the high compression ratios and compression loads typically generated in conventional heavy fuel engines. For example, U.S. Pat. Nos. 4,977,873, 5,109,817, 5,297,518 and 5,421,299 disclose catalytic igniters having a catalyst material wound about an igniter rod which generally is heated to typically around 1200.degree. C. The problem with such igniters has been reliability as the igniter rods are subjected to vibration during engine operation and as current is passed through the catalyst wire wound thereabout, which has caused the rods to crack or break, causing failure of the igniter. In addition, it still has been necessary to significantly compress the diesel fuels to try to form vapors that can be readily ignited by the igniter.
Accordingly, it can be seen that a need exists for a low cost internal combustion engine capable of being operated using multiple different types of fuels including less volatile heavy fuels such as JP5, JP8, Jet A, diesel fuel and kerosene based fuels, which is able to ignite such heavy fuels at reduced compression ratios so as to enable the engine to be constructed of lighter weight components and be easily portable without a significant loss of power output by the engine.